Adiabatic thermokinetics and process safety of pyrotechnic mixtures

Pyrotechnic mixtures are susceptible to explosive decompositions. The aim of this paper is to generate thermal decomposition data under adiabatic conditions for fireworks mixtures containing potassium nitrate, barium nitrate, sulfur, and aluminum which are manufactured on a commercial scale. Differential scanning calorimeter is used for screening tests and accelerating rate calorimeter is used for other studies. The self heat rate data obtained showed onset temperature in the range of 275?C295?°C for the fireworks atom bomb, Chinese cracker and palm leaf cracker. Of the three mixtures studied, atom bomb mixture had an early onset at 275?°C. The mixtures in general showed vigor exothermic decompositions. Palm leaf mixture exhibits multiple exotherm and reached a final temperature of 414?°C. The thermal decomposition contributes to substantial rise in system pressure. The heats of exothermic decomposition and Arrhenius kinetics were computed. The kinetic data are validated by comparing the predicted self heat rates with the experimental data.     

Reaction of Potassium Fluoride in the Presence of Tetraalkylammonium Halides. Preparation of Acylfluorides and Fluoroformates

Acyl fluorides are usually prepared from the corresponding chlorides by halogen exchange. High temperatures are necessary with potassium fluoride (1). The use of potassium bifluoride (2), thallium fluoride (3) or amines-fluorhydric acid complexes (4,5,6) allowed the reaction to occur in milder conditions. Addition of fluoroketones (7) or ether-crowns (8) increased the activity of potassium fluoride.     

A study of the titrimetric potassium silicofluoride method for determination of silica in aluminosilicate materials

A critical study of the titrimetric potassium silicofluoride method for determination of silica reveals that quantitative precipitation of the sificofluoride is possible in 3.5-7.5N acid containing 1% sodium fluoride and >/ 12% potassium chloride. An aqueous wash solution (pH approximately 5.3) containing 0.1% sodium fluoride and 12% potassium chloride has been found ideal for washing the precipitate without significant hydrolysis even at 35 degrees C. The interference of large amounts of aluminium (up to 160 mg of Al(2)O(3)) is eliminated by precipitating the silicofluoride in 6-7.5N acid solution, the aluminium then forming practically no fluoro-complex, because of extensive protonation of fluoride. Interference by large amounts of boron (up to 160 mg of B(2)O(3)) is eliminated by precipitating silicofluoride with the minimum permissible potassium chloride concentration (12%) and washing with the aqueous wash solution at room temperature. Nitrazene Yellow has been used as a more sensitive indicator.     

Direct determination of fluoride in aluminium reduction materials by using an ion-selective electrode

Macro amounts of fluoride in aluminium reduction materials are successfully determined with a fluoride electrode. Except for anhydrous aluminium fluoride, which requires fusion with sodium hydroxide, samples are dissolved in aqueous media. Cryolite and sodium fluorosilicatc are dissolved in boiling sodium hydroxide solution. Other materials containing fluoride, such as fluorspar and the reduction cell bath and pot-lining, require dissolution in a hydrochloric acid solution of aluminium chloride. Potential interference from large amounts of aluminium (and calcium, if present) is eliminated and pH control attained by using ammoniacal sulphosalicylate (and EDTA). The procedures are reasonably rapid. Relative errors of less than 2% and a relative standard deviation of 1% are achieved.     

The synthesis of fluoroether-fluorosilicone hybrid polymers

The replacement of the fluorocarbon segment in the general class of hybrid fluorocarbon-fluorosilicones by fluoroether units was investigated in order to improve low temperature properties without sacrificing high temperature performance. The effects of the co-reactant halogens (bromine and iodine) and metallic fluorides (potassium fluoride and cesium fluoride) on the product yields in the syntheses of the requisite α,ω-dihalo-F-ether intermediates [1] from the corresponding acyl or diacyl fluorides were studied. While a better yield was obtained with bromine than with iodine, the iodoperfluoroethers produced superior yields in the subsequent ethylene addition reactions, as expected. Potassium fluoride was preferable to cesium fluoride in the synthesis of the iodo-F-ethers, since cesium fluoride effects decomposition of the ethers.     

Determination of organic peracids and hydrogen peroxide in mixtures

A simple method for the determination of organic peracids and hydrogen peroxide in mixtures is presented. The method is based on the instantaneous reaction of peracids with neutral potassium iodide and on the formation of a stable complex between hydrogen peroxide and titanyl ions. This complex is decomposed with sodium fluoride and the ensuing reaction with iodide is accelerated with molybdic acid. The influence of the different additives on the analytical results has been studied.     

Oxidative degradation and pyrolysis of polyvinyl chloride in binary mixtures of the system K,Na, Ca ‖ NO3, NO2, OH

Oxidative degradation and pyrolysis of polyvinyl chloride in the temperature range 200–500°C in binary mixtures containing sodium, potassium, and calcium nitrates and nitrites and calcium hydroxide were studied. A scheme of oxidative degradation of polyvinyl chloride and of binding of chlorine and carbon present in the polymer in the reactions of the degradation products with the mixture components was suggested.     

Differential thermal analysis and temperature profile analysis of pyrotechnic delay systems: mixtures of tungsten and potassium dichromate

The self-propagating combustion reaction between tungsten and potassium dichromate has been studied by differential thermal analysis and temperature profile analysis. Two reaction stages have been distinguished in the combustion where the rate of temperature rise is ? 10⁵ K min^?1: in the first potassium dichromate is reduced by tungsten to form potassium chromate and in the second stage the potassium chromate reacts with more tungsten to form potassium tungstate and chromic oxide.     

Field determination of fluoride in drinking water using a polymeric aluminium complex of 5-(2-carboxyphenylazo)-8-hydroxyquinoline impregnated paper

A simple field method which allows the determination of fluoride in drinking water with a small handheld instrument called Arsenator was developed. Arsenator is a commercially available instrument which was used successfully for reliable determination of arsenic. In the proposed method the functionality of the Arsenator which is based on a photometric measurement of a spot on the reagent paper is expanded to analyse fluoride. A polymeric aluminium complex of 5-(2-carboxyphenylazo)-8-hydroxyquinoline (LH₂) has been prepared as a new specific reagent for fluoride. Job's method of continuous variation was adopted for the determination of the composition of the coloured complex, which was further characterized by UV-VIS spectroscopic studies. The molar absorptivity of the complex formation is 8.48?×?10³?L?mol^?1?cm^?1 at 410?nm. The coloured complex reacts with fluoride on an impregnated paper where its colour changes are dependent on the concentration of fluoride in water samples. The change in the colour was measured using the Arsenator. The method allows a reliable determination of fluoride in the range 0.3 to 2.0?mg?L^?1. Further spectophotometric determinations of fluoride in drinking water were also studied. The determination is based on the reaction of aluminium complex with fluoride in the examined samples. Beer's law is obeyed in the range 0.3 to 2.0?mg?L^?1 of fluoride at 495?nm. Sensitivity, detection limit and quantitation limit of the method were found to be 0.251?±?0.007?µg^?1?mL, 0.1?mg?L^?1 and 0.3?mg?L^?1, respectively. The optimum reaction conditions and other analytical conditions were evaluated. The effect of interfering ions on the determination is described. There is no interference by nitrate or chloride. Sulphate interfered only at high concentrations which are not expected in drinking water.     

Reaction of sulphuryl chlorofluoride with a few metals and metal oxides

Sulphuryl chlorofluoride has no observable reaction with metals and metal oxides at room temperature. Metals like copper, silver, iron, and zinc react with the chlorofluoride in the temperature range 200–400°C. Metal chlorides, metal fluorides and sulphur dioxide are the main products of these reactions. With the corresponding metal oxides, on the other hand, the respective metal sulphates are formed in addition to the metal chlorides and fluorides. In the case of lead and lead oxide, lead chlorofluoride is formed instead of lead chloride and lead fluoride. Sulphuryl fluoride is formed in small quantities in all these reactions by the decomposition of the chlorofluoride. Glass is not attacked by sulphuryl chlorofluoride below 500°C.During the course of our investigations on the reactivity of sulphuryl chlorofluoride, it is observed that sulphuryl chlorofluoride does not react with glass up to 500° C. However, it reacts with metals and metal oxides between 200° to 400° C. The reaction products with metals are the corresponding metal chlorides, metal fluorides and sulphur dioxide. With the oxides, in addition to the metal chlorides and metal fluorides, metal sulphates are formed. The results of these investigations are presented in this communication.     

Cryolite precipitation by the Reaction of aluminium salt with sodium fluoride in aqueous solution

When aqueous solution of aluminium salt involving nitrate, chloride or sulfate was added into sodium fluoride solution, an immediate reaction occured to form cryolite-like precipitate. Examination into the resultant solution and analysis for the precipitate were carried out, leading to the fact that fluorine ion can substitute for bound water molecules around central Al⁺⁺⁺ ion, but hardly for bound hydroxide and sulfate ion which should go or be “frozen”, as it is, into cryolite-like precipitate. These ligand substitution reaction seems to contribute to identification of ion species of aluminium in aqueous solution.     

Determination of fluoride with thorium nitrate by catalytic titration

Amperometry, constant-current potentiometry and spectrophotometry were used to follow the course of catalytic titrations of fluoride and silicofluoride with thorium nitrate. The hydrogen peroxide-iodide system was used as the indicator reaction. Titrations were performed in 50% ethanolic acetate buffer, pH 3.6. Amounts of 3.70-6.85 mg of ammonium fluoride, 5.53-10.79 mg of potassium fluoride and 4.34-8.41 mg of sodium silicofluoride were determined with a maximum average deviation of 0.9%. The results obtained are in good agreement with those of comparable methods.     

The monitoring of fluoride in ambient air by fluoridation rate candles

The determination of fluoridation rate provides a relatively inexpensive time-average surveillance method for monitoring atmospheric fluorides in specific areas. The fluoride is collected by the reaction with calcium oxide coating on a filter paper strip during the exposure of the candle to ambient air. The collected fluorides are then extracted from the exposed filter paper into a buffer solution and subsequently determined by ion selective electrode.     

Isothermal titration calorimetry and molecular dynamics study of ion-selectivity in mixtures of hydrophobic polyelectrolytes with sodium halides in water

Aliphatic x,y-ionenes are polyelectrolytes in which x and y denote the numbers of methylene groups separating quaternary ammonium ions. They represent useful model substances for studying hydrophobic and charge effects in aqueous solutions. We used isothermal titration calorimetry to measure the enthalpies of mixing, ΔH(mix), of 3,3- and 6,6-ionene fluorides and bromides with low molecular weight salts (NaF, NaCl, NaBr, and NaI) at 298 K in water. The signs and magnitudes of the measured enthalpies depend on the hydrophobicity of the ionene and on the nature of the added salt. For example, addition of sodium fluoride to solutions of 3,3- and 6,6-ionene fluorides produced endothermic effects, while addition of sodium bromide to 3,3-ionene bromide resulted in a strong exothermic effect. Interestingly, mixing of 6,6-ionene bromide and NaBr solutions in water gave a small exothermic heat effect. Polyelectrolyte theories, based on continuum-solvent models, predict enthalpies of mixing to be positive (endothermic) for all the solutions examined in this work. The ion-specific effect is more strongly expressed in ionene solutions with higher charge density (3,3-ionene). The most important result of this work is the finding that the enthalpy of mixing of 3,3- (and of 6,6-ionene) fluorides with sodium halides can be expressed as a linear function of the enthalpy of hydration of the halide counterions. The experimental results were complemented with an explicit water molecular dynamics simulation of solutions of oligoions modelling 3,3- and 6,6-ionenes. The computer simulation results for various nitrogen-counterion pair distribution functions were in most cases consistent with the enthalpy measurements.     

Determination of total fluorine in vegetables and plants by open-flame ashing and microdiffusion : Comparison with furnace ashing and oxygen-flask combustion

The sample is ashed in a nickel crucible over an open flame with calcium hydroxide as the fixative; fluoride is separated by micro-diffusion and measured with a fluoride-selective electrode. The calcium hydroxide fixative permits a temperature of 800–850°C during the final ashing, so that insoluble silicates are decomposed and fluoride is converted to an acid-soluble form. Other advantages over furnace ashing at 600°C are less contamination and more rapid ashing (20 min compared to 6 h). The interference of aluminium and silica on microdiffusion was studied: perchloric acid was found to be preferable to sulphuric acid as medium. A new way for preparing calcium hydroxide suspension, low in fluoride, is described. The values found by the proposed method generally compare well with those obtained by oxygen flask combustion. Direct diffusion (i.e. without ashing) gave much lower values than the ashing methods, except for tea leaves.     

Synthesis of sodium tungstate from the system Na<Subscript>2</Subscript>C<Subscript>2</Subscript>O<Subscript>4</Subscript>-NaNO<Subscript>3</Subscript>-WO<Subscript>3</Subscript>

The physicochemical basis of the heterogeneous reaction between the components of the system (sodium oxalate)-(sodium nitrate)-(tungsten(VI) oxide) has been studied. The reaction of WO₃ with sodium oxalate-nitrate mixtures occurs at a lower temperature and at a higher rate than the reaction with pure sodium carbonate. A high-yield process for the synthesis of high-purity sodium tungstate has been developed on the basis of this study.     

1,1,3,3,3-Pentafluoropropene secondary amine adducts new selective fluorinating agents

Addition of secondary amine SA (dimethylamine DMA, diethylamine DEA, pyrrolidine Pyr, piperidine Pip, morpholine Mor) to pentafluoropropene PFP gives rise to generation of mixtures of two products (1-dialkylamine-1,3,3,3-tetrafluoropropene and N,N-dialkyl-1,1,3,3,3-pentafluoropropylamine) in different ratios. Those reaction mixtures, however, were found to be efficient fluorinating agents replacing hydroxyl groups in alcohols into fluorine. In general, they react with alcohols yielding corresponding fluorides, equimolar amounts of appropriate 3,3,3-trifluoropropionamide and hydrogen fluoride. Aliphatic primary alcohols including octanol and benzylic alcohol yield only alkyl fluorides. The secondary and tertiary alcohols, beside the desired fluorides, give usually considerably amount of alkenes.     

Differentiation of Spanish brandies according to their metal content

Eleven metals, namely, aluminium, calcium, cadmium, copper, iron, lead, magnesium, manganese, potassium, sodium and zinc were determined in twenty samples of Sherry brandies and twelve samples of Penedés brandies by applying atomic spectrometry techniques. Flame atomic absorption spectrometry was used for quantitating calcium, copper, iron, magnesium, manganese and zinc; atomic emission spectrometry to determine potassium and sodium; and graphite furnace atomic absorption spectrometry to analyse aluminium, cadmium and lead. A chemometric approach was followed to study the discrimination between brandies from Sherry or Penedés according to the metal profile.     

Reactions of HCl and D2O with molten alkali carbonates

The acidic oxide SO? and protic acid HCl are among the gases released in the combustion of coal and the incineration of municipal waste. They are typically removed by wet or dry scrubbing involving calcium carbonate or calcium hydroxide. The molten alkali carbonate eutectic provides a liquid-state alternative that readily absorbs SO? and HCl and does not become covered with a passivating layer. Gas-liquid scattering experiments utilizing the eutectic mixture (44 mol % Li?CO?, 31 mol % Na?CO?, 25 mol % K?CO?) reveal that the reaction probability for HCl(g) + CO?2? → CO?(g) + OH? + Cl? is 0.31 ± 0.02 at 683 K and rises to 0.39 at 783 K. Gaseous CO? is formed within 10?? s or less, implying that the reaction takes place in a liquid depth of less than 1000 ?. When the melt is exposed to D?O, the analogous reaction D?O(g) + CO?2? → CO?(g) + 2OD? occurs too slowly to measure and no water uptake is observed. Together with previous studies of SO?(g) + CO?2? → CO?(g) + SO?2?, these results demonstrate that molten carbonates efficiently remove both gaseous HCl and SO? while reacting at most weakly with water vapor. The experiments further highlight the remarkable ability of hot CO?2? ions to behave as a base in reactions with protic and Lewis acids.     

Sulfonyl fluoride-based prosthetic compounds as potential (18) f labelling agents

Nucleophilic incorporation of [(18) F]F(-) under aqueous conditions holds several advantages in radiopharmaceutical development, especially with the advent of complex biological pharmacophores. Sulfonyl fluorides can be prepared in water at room temperature, yet they have not been assayed as a potential means to (18) F-labelled biomarkers for PET chemistry. We developed a general route to prepare bifunctional 4-formyl-, 3-formyl-, 4-maleimido- and 4-oxylalkynl-arylsulfonyl [(18) F]fluorides from their sulfonyl chloride analogues in 1:1 mixtures of acetonitrile, THF, or tBuOH and Cs[(18) F]F/Cs(2) CO(3(aq.)) in a reaction time of 15?min at room temperature. With the exception of 4-N-maleimide-benzenesulfonyl fluoride (3), pyridine could be used to simplify radiotracer purification by selectively degrading the precursor without significantly affecting observed yields. The addition of pyridine at the start of [(18) F]fluorination (1:1:0.8 tBuOH/Cs(2) CO(3(aq.)) /pyridine) did not negatively affect yields of 3-formyl-2,4,6-trimethylbenzenesulfonyl [(18) F]fluoride (2) and dramatically improved the yields of 4-(prop-2-ynyloxy)benzenesulfonyl [(18) F]fluoride (4). The N-arylsulfonyl-4-dimethylaminopyridinium derivative of 4 (14) can be prepared and incorporates (18) F efficiently in solutions of 100?% aqueous Cs(2) CO(3) (10?mg?mL(-1) ). As proof-of-principle, [(18) F]2 was synthesised in a preparative fashion [88(±8)?% decay corrected (n=6) from start-of-synthesis] and used to radioactively label an oxyamino-modified bombesin(6-14) analogue [35(±6)?% decay corrected (n=4) from start-of-synthesis]. Total preparation time was 105-109?min from start-of-synthesis. Although the (18) F-peptide exhibited evidence of proteolytic defluorination and modification, our study is the first step in developing an aqueous, room temperature (18) F labelling strategy.